A few years ago, Christos Tsirogiannis was looking through the Metropolitan Museum of Art's online collection when he had a flash of recognition. While studying an ancient Hellenic krater something 'suddenly clicked'. The vase was decorated with a painting of Dionysos, and he knew that he had seen the subject on that krater before. This led to a startling realization: the krater came from a seized private collection of looted items, and it wasn't the only one. National Geographic's Nick Romeo tells the story.

Greek-born archaeologist Christos Tsirogiannis

A forensic archaeologist affiliated with the University of Glasgow’s Scottish Centre for Crime and Justice Research, Tsirogiannis has access to restricted databases containing tens of thousands of photographs and documents seized during raids. Searching through the online archives, he found five photos of the Met’s Greek krater among items confiscated from Giacomo Medici, an Italian antiquities dealer convicted in 2005 of receiving stolen goods and conspiracy to traffic looted antiquities.

So why was an object that may have been dug up and sold by looters on display at a famous American museum, and how did it get there? Uncomfortable questions like these are becoming more common in the digital age as museums, universities, and private collectors publish online catalogs of their collections, creating a valuable resource for anti-looting detectives like Tsirogiannis.

Although his influence is rarely acknowledged, Tsirogiannis’s sleuthing has spurred major museums and auction houses in the United States, Europe, and Asia to return dozens of treasured objects to their rightful owners in Greece, Italy, and other countries.

“I always liked jigsaw puzzles as a kid. My work now resembles a gigantic jigsaw puzzle made of thousands of smaller puzzles.”

After studying archaeology and art history at the University of Athens, Tsirogiannis worked for the Greek Ministries of Culture and Justice dating and classifying looted artifacts. He earned a doctorate at Cambridge University in 2013, writing his dissertation on international networks of illicit antiquities traders.

With a voluminous visual memory that can call to mind thousands of images of looted artifacts—and a willingness to send dozens of emails that are never answered—Tsirogiannis is actively researching hundreds of objects from museums around the world. He recently tipped off authorities in Manhattan that an Etruscan vessel displayed at a Midtown gallery was stolen, leading to its repatriation, or official return, to Italy.

In the case of the Dionysus krater at New York's Metropolitan Museum of Art, photos seized from Giacomo Medici, the convicted antiquities dealer, show the vase crusted with soil and salt, literally fresh from the earth. Because Medici took Polaroid photos—a technology not available in Europe until 1972—Tsirogiannis knew that the krater was dug up after 1970, the year a major UNESCO treaty made it illegal to export cultural property from signatory nations.

In 1989 the krater turned up at Sotheby's, where it sold at auction for $90,000. Like other major auction houses, Sotheby’s doesn’t reveal the names of consignors or buyers and declined to speak on the record for this article. But the Metropolitan Museum added the krater to its collection soon after Sotheby's sold it.

The Met’s website states that the krater was acquired by the Bothmer Purchase Fund. Dietrich von Bothmer was a longtime Met curator who died in 2009. Interrogations of convicted antiquities dealers, and evidence from their confiscated archives, have established that Bothmer was one of their regular clients. Forty fragmentary artifacts from Bothmer’s collection at the Met have been returned to Italy since 2005.

The Odd Couple of Antiquities & Art Theft A former art smuggler and the former head of the Art and Antiquities Squad of the British Police join forces to expose the illegal smuggling of ancient treasures, a multi-billion dollar business. Once Tsirogiannis identified the origin of the Dionysus krater, he promptly sent multiple emails to valid addresses at the Met. He received no reply, and the vase remains on display in Gallery 161 of the museum.

The Met’s only comment for this story was opaque: "The Museum has been in touch with the Italian Ministry of Culture regarding the Terracotta Bell Krater (1989.11.4)". The museum’s acquisitions policy states that before purchasing an object curators will investigate "whether the work of art appears in relevant databases of stolen works and the circumstances under which the work of art is being offered to the museum".

Tsirogiannis is skeptical about the stated intentions of the Met and other museums.

“They hang on to illicit objects as long as they can, until someone finds out. It’s all about money, fame, and ownership.”

There are approximately 10,000 fragments from the Bothmer collection that haven’t yet been published online, and the Met has declined to say when they might be published. It’s unclear how many of the fragments might match pieces in other museums’ collections or recorded in criminal databases. But when they do go online, it’s likely Tsirogiannis and other detectives like him will be watching.